1. Field of the Invention
The present invention relates to an all-optical gate for carrying out an AND logic operation. Such a gate might be used, for example, in an optical telecommunications system, or in optical data-processing devices.
2. Related Art
AND is a fundamental logic operation necessary for example, for the implementation of optical networks including photonic switching nodes. Our co-pending international application no PCT/GB94/00397, the contents of which are incorporated herein by reference, describes and claims one example of the use of an AND function in recognising an address carried in the header of a frame on the optical network, and controlling a routing switch accordingly.
It has recently been proposed to use the process known as four-wave mixing (FWM) to implement an AND function. FWM produces an output proportional to the product of the electric fields of two input optical signals. Andrekson et al: "16 Gbit/s All Optical Demultiplexing Using Four-wave Mixing," Electron. Lett., 27, 1991, pp. 922 and R. Schnable, W. Pieper, R. Ludwig, H. G. Weber: "All Optical AND Gate using Femtosecond Non-linear Gain Dynamics in Semiconductor Laser Amplifiers", ECOC '93 describe implementations of AND functions using FWM in single-mode optical fibre and in semiconductor laser amplifiers (SLAs) respectively. Potentially such devices might be appropriate for switching or logic processing functions in optical telecommunications networks. However, the optical-fibre based devices require long interaction lengths, and so have a large in-built switch latency. This latency makes such devices unsuitable for applications where a fast decision time is required. SLAs by contrast have short device lengths, and hence low latency and are capable of high switching speeds due to their non-linear gain dynamics.